Comparative Analysis of Myeloperoxidase Deficiency in Humans and Mice: Conserved and Species-Specific Effects on Neutrophil Biology

M. Ahdab (Köln)¹, H. Guthoff (Köln)¹, N. Nix (Köln)¹, S. Derman (Köln)², A. G. Barbe (Köln)², H. Nemade (Köln)³, E. S. Philip (Köln)³, K. Singgih (Köln)³, K. Nellessen (Köln)¹, A. Hüttermann (Köln)¹, A. Paunel-Görgülü (Köln)⁴, C. Diekmann (Köln)³, P. Schelemei (Köln)³, J.-W. Lackmann (Köln)⁵, S. Müller (Köln)⁵, W. Johannis (Köln)⁶, T. Streichert (Köln)⁶, S. Baldus (Köln)¹, H. Winkels (Köln)³, P. von Stein (Köln)¹, M. Mollenhauer (Köln)³, A. Hof (Köln)^1
1Universitätsklinikum Köln Klinik III für Kardiologie, Angiologie, Pneumologie und Internistische Intensivmedizin Köln, Deutschland; ²Universitätsklinikum Köln Poliklinik für Zahnerhaltung und Parodontologie Köln, Deutschland; ³Universitätsklinikum Köln Klinik III für Innere Medizin - Experimentelle Kardiologie Köln, Deutschland; ⁴Universitätsklinikum Köln Klinik und Poliklinik für Herz- und Thoraxchirurgie, Herzzentrum Köln, Deutschland; ⁵Universität zu Köln Center for Molecular Medicine Cologne Köln, Deutschland; ⁶Universitätsklinikum Köln Institut für Klinische Chemie Köln, Deutschland

Background:
Cardiovascular diseases are the leading global cause of death, with vascular inflammation as a key driver of disease progression. Myeloperoxidase (MPO) is a neutrophil-derived heme enzyme that generates reactive oxidants and regulates key effector functions including oxidative burst and neutrophil extracellular trap formation. It has been widely implicated in cardiovascular inflammation and is considered a potential therapeutic target. However, substantial interspecies differences in neutrophil biology, including MPO expression levels and granule composition challenge translation of preclinical findings into patients. Consequently, molecular effects observed in Mpo^⁻/⁻ mice may not fully reflect human physiology, limiting predictive value for therapeutic development.

Methods & Results:
We systematically screened 11,608 patients for reduced MPO activity using the ADVIA 2120i system and identified 282 individuals with low MPO activity. 56 subjects met inclusion criteria. Based on neutrophil MPO protein content, patients were stratified into persistently MPO-deficient (MPO^low, n=12) and transiently MPO-deficient (MPO^rec, n=44) and compared with 20 matched MPO-competent controls. PMN purity was confirmed by flow cytometry in human and murine samples. MPO levels and activity were measured by ELISA, Western blot, Tetramethylbenzidin-based peroxidase and Nitric oxide (NO)-consumption assay. 

MPO^low individuals exhibited significantly reduced neutrophil MPO protein abundance, enzymatic activity, and circulating MPO plasmalevels, with two individuals showing near-complete absence of detectable MPO protein without overt immunodeficiency. The estimated point prevalence of persistent MPO deficiency was approximately 1:200.

To define conserved and species-specific consequences of MPO loss, we performed shotgun proteomics of human MPO^low and murine Mpo^⁻/⁻ PMN. Humans exhibited 204/2,084 differentially expressed proteins, whereas mice showed 599/4,265 altered proteins. PANTHER subclassification demonstrated that both species exhibited similar functional annotations despite markedly different underlying protein class distributions, including immunity proteins (PC00090), intercellular signaling molecules (PC00207) and transmembrane signal receptors (PC00197), indicating that conserved biological outputs are achieved through distinct protein networks across species.

Despite partial conservation of innate immune and oxidative stress pathways, GO-Term Enrichment  and Reactome Pathway Analysis showed pronounced species-specific divergence in PMN signaling architecture: in Mpo^low, MPO deficiency was associated with dysregulation of complement activation, coagulation, humoral immunity and MAPK/JNK signaling, whereas murine Mpo^⁻/⁻ PMN were predominantly characterized by enrichment of phagocytosis, chemotaxis and Rho GTPase signaling pathways.

Conclusion:
Persistent human MPO deficiency results in markedly reduced enzyme abundance. MPO deficiency leads to broadly conserved alterations in neutrophil immune and stress responses across humans and mice indicating that MPO’s oxidant chemistry is largely conserved. However, similar functional outcomes may involve different signaling pathways in each species contributing to divergent phenotypes in disease models. These findings underscore species-specific mechanisms in MPO-related neutrophil biology and highlight critical considerations for translating MPO-targeted therapies from animal models to human disease.